Charging of a scrap into a processing furnace used for melting a metallic material, refining a molten metal, etc, such as an arc furnace, is carried out generally in the following way.
The scrap is charged in advance into a container referred to as a "bucket" and this bucket is transported to a position near the arc furnace by a ceiling crane. A turnable furnace cover is provided to the arc furnace. When the scrap is charged, this furnace cover is turned and opened. Then, the bucket is moved onto the furnace and the bottom portion of the bucket is opened so as to charge the scrap into the furnace.
Charging of the scrap into the arc furnace is carried out, in a batch-method, twice or thrice per heat. According to this method, however, the problem is that the furnace cover must always be opened at the time of charging of the scrap and consequently, heat radiation from the furnace is great. Another problem is that an operation environment is deteriorated due to the generation of dust, etc.
Accordingly, various methods of continuously charging scrap have been proposed as methods of charging scrap into the furnace without opening the furnace cover. In the furnace operation in this case, a melting operation is started while a suitable amount of a molten steel is left over from the previous tapping operation. Therefore, the operation is carried out in the conventional refining state from the initial stage of melting.
In the operation in the condition of the refining stage, it becomes very important to suitably maintain the thickness of a slag on the molten steel in order to improve arc heat efficiency, and generally, this is effected by the generation of a CO gas resulting from the reaction of carbon and oxygen. Consequently, the quantity of the gas generated from the furnace becomes greater than in the conventional method. In other words, a technology of efficiently recovering the heat of the exhaust gas becomes important. Japanese Unexamined Patent Publication (Kokai) No. 4-42452, for example, discloses a technology of charging scrap into a furnace by introducing the exhaust gas into a scrap conveyor having a flue formed therein and passing the exhaust gas in a counter-flow arrangement to the movement of the scrap so as to pre-heat the scrap.
However, such a scrap conveyor has the construction wherein the exhaust gas flows above the scrap inside the conveyor having the flue formed thereon. Since pre-heating of the scrap is applied only to the surface layer portion of the scrap and heat is not sufficiently transferred to the scrap in the lower layer portion. To raise the pre-heating temperature, therefore, it is necessary to either enlarge the transverse width of the conveyor so as to enlarge the heat transfer area, or to elongate the length of the conveyor so as to secure a long pro-heating time. In other words, a problem develops in that the setup becomes greater in size.
Further, a gas seal is difficult at a portion at which the scrap on the conveyor enters the flue, and external air is sucked simultaneously with the suction of the exhaust gas. Accordingly, dust collection efficiency drops, as well.
Also, each of U.S. Pat. No. 3,301,662 (FIGS. 1 to 6) and European Patent Publication No. 420,776 (FIG. 1) discloses a conveyor for feeding scrap to a processing furnace while preheating the scrap by the exhaust gas from the said furnace. The conveyor is covered by a gas seal cover and a flue is formed between the cover and the scrap on the conveyor, the exhaust gas being introduced into the flue. An exhaust gas passage portion or suction space is present below the conveyor, an exhaust gas suction duct opening to the gas passage portion or suction space such that the exhaust gas inside the flue passes through the scrap on the conveyor and is sucked and discharged.
However, none of the above references describe that a scrap reception hopper having upper and lower covers capable of being opened and closed is disposed above a scrap charging portion of said scrap conveyor, a tapping device for said scrap conveyor is disposed below said hopper, and peripheries of said hopper, said tapping device and the conveyor are covered with a gas seal cover and that an exhaust gas passage portion is disposed between a bottom plate and side plate of the conveyor.